Many restaurants and food service providers provide coffee and other beverages into which a small volume of creamer or other liquid is added. The prior art dispensers for such liquids open a valve for a time period that is determined using an initial level of the liquid in the container. As liquid is dispensed over time, the level of the liquid in the tank drops of course, lowering the static pressure at the valve and as a result, reducing the volumetric flow rate from the tank.
Some prior art creamer dispensers are able to dispense different fixed amounts of liquid by actuating one or more push button switches on the front panel of the device. The switches send a signal to a computer or other controller, which opens an electrically-actuated dispensing valve for a time period that is supposed to allow the volume of liquid that was requested by the actuation of a push button to be dispensed from a bulk container. Such prior art dispensers require a user to accurately fill the container and specify the starting volume to a controller. The controller calculates dispensing valve open times for each dispensing using the starting or initial liquid level. Prior art devices account for the continuously-dropping static pressure by counting the number of ounces that are requested to be dispensed from the container. The number of ounces that are requested is used to decrement an initial amount of liquid in the container. The volume dispensing accuracy of prior art devices thus depends in part on the accuracy of the initial level that is provided to the controller.
Electromechanical closure of a pinch valve is typically accomplished by activating a solenoid to draw a spring-biased bar or gate against an elastomeric sleeve or tube, thereby cutting off fluid flow through the tube or sleeve. Some prior art pinch valves are fluid actuated wherein the pinching action is accomplished by air or hydraulic pressure placed on the elastomeric sleeve or tube.
A problem with prior art pinch valves, especially those used with food and liquid dispensers, is that they do not facilitate the installation and removal of a bulk container. Stated another way, prior art pinch valves typically require disassembly to install and/or remove a tube passing through them and also for cleaning.
A problem with liquid dispensers that count the number of dispensing actuations, or which decrement a user-specified starting amount in a container according to the number of dispensing actuations, is that their accuracy depends largely on whether the initial amount of liquid in a container was accurate. If the actual starting level in the container is not what is conveyed to the controller when the container is first installed, every subsequently dispensed volume will not be equal to the requested amount.
Another problem with prior art dispensers is that dispensing accuracy almost invariably deteriorates as the level of the liquid in a container falls with successive dispenses. Dispensing valves require a finite amount of time to open and close. Different valves can require slightly different amounts of time to open and close. The amount of liquid actually dispensed rarely matches the amount of liquid that is supposed to be dispensed. Over time, the dispensing error accumulates. As the liquid level in a container approaches zero, the amount of liquid that is actually dispensed for any specified valve open time period will almost always be different from what the dispenser counts or thinks was dispensed. A liquid dispenser that is able to more accurately dispense user-specified volumes without regard to an initial or starting volume and which can continue to do so as a tank empties would be an improvement over the prior art.